1. Field of the Inventions
The present inventions relate to engines, and more particularly to engines, which can both purify exhaust gas and maintain higher power output.
2. Description of the Related Art
It is common to place one catalyst device in an exhaust system of an engine for purifying exhaust gas. It is preferable that such a catalyst device be disposed as far as possible from an exhaust opening of the engine from a viewpoint of preserving the power output and performance of the engine. On the other hand, the device catalyst should also be disposed as close as possible to the exhaust opening of the engine from a viewpoint of the exhaust gas purification, e.g., preserving the high temperature of the exhaust gas for heating the catalyst device.
One design, which responds to the aforementioned contradictory concerns, is disclosed, for example, in Japanese Patent Document JP-A-Hei 10-176523. In this conventional device, a switching valve 12 is provided within an exhaust pipe, and divides the exhaust passage into two systems 10 and 11. A catalyst 14 is placed within an exhaust passage 10, and a catalyst 17 is placed downstream of the catalyst 14.